#3553: parallel gc suffers badly if one thread is descheduled -------------------------------------+------------------------------------ Reporter: simonmar | Owner: simonmar Type: bug | Status: closed Priority: normal | Milestone: 6.12.2 Component: Runtime System | Version: 6.10.4 Resolution: fixed | Keywords: Operating System: Unknown/Multiple | Architecture: Unknown/Multiple Type of failure: None/Unknown | Difficulty: Unknown Test Case: | Blocked By: Blocking: | Related Tickets: -------------------------------------+------------------------------------ Comment (by tibbe):

I noticed that if I change nofib/parallel/ray to do its work in a separate thread (see diff), that this "last core slowdown" completely vanishes. Can anybody explain this massive variance?

It could be because main runs in a bound thread. Why that makes a huge difference I'm not sure (more context switching?), but that's a likely cause. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/3553#comment:11 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler